1. Field of the Invention
The present invention concerns a magnetic resonance system of the type having a magnet system that generates a magnetic field in an excitation region, allowing nuclei in an examination subject in the excitation region to be excited to emit a magnetic resonance signal, and a reception antenna device with a number of local coils for reception of the magnetic resonance signal, in proximity to the examination subject, and that has a base part and an attachment part; the attachment part being attached to the based part such that the examination subject is located between the base part and the attachment part; with the local coils being respectively connected with an evaluation device for evaluation of magnetic resonance signals.
2. Description of the Prior and Related Subject Matter
Magnetic resonance systems of the above type are generally known.
Conventionally, the acquisition of magnetic resonance signals emitted from the examination subject ensues either with a whole-body antenna or with local coils. If the magnetic resonance signal is acquired with a whole-body antenna, the magnetic resonance signal can be acquired from the entire excitation region. The acquisition, however, may occur only with relatively low signal-to-noise ratio (SNR). Therefore local coils are also used in many cases in magnetic resonance systems, often multiple local coils. The local coils are arranged near to the examination subject (normally a person) and can therefore receive signals with a good SNR, although only from a small part of the excitation region. Moreover, spatial coding by gradient fields can be supplemented due to spatial resonance by the arrangement of the local coils as such. The required measurement time for an acquisition thus can also be reduced.
In conventional magnetic resonance systems, all local coils are connected by a corresponding number of connectors (attached to the patient bed) and a movable cable harness to an evaluation device that is arranged on the base body. Due to the attenuation of the long, thin cables employed, preamplifiers must be arranged in the local coils. Furthermore, each local coil must have a detuning circuit that deactivates the coil given non-use and upon transmission. Elaborate common mode chokes (known as sheath wave barriers) must also be inserted into the long cable harness in order to be able to limit induced voltages during transmission.
A plug connection for local coils that operates without contact (namely via inductive coupling) is known from DE 101 30 615 C2. This teaching represents an advance since a galvanic contact between the local coil and the evaluation device is no longer necessary for coupling of a local coil to the evaluation device. As is conventional, however, the necessity exists of actively plugging the connection by operating personnel. The local coil must also be specifically connected to the evaluation device or disconnected from it.
From DE 35 00 456 C2 it is known to couple a local coil with the whole-body antenna. A contact-free coupling is achieved, but this coupling is possible only for a single local coil, and even then only given suitable orientation of the local coil. Moreover, the teaching of DE 35 00 456 C2 can not be extended to multiple local coils. Here as well the local coil must also be actively connected to the whole-body antenna or disconnected from it.
From EP 0 437 049 A2 it is known to directly, inductively couple a local coil to another coil that is arranged in immediate proximity of the local coil. For this purpose the local coil must also be actively connected to the evaluation device or disconnected from it.
An approach to overcome the mechanical plug connection between the electrical circuits of the moving part and the stationary base part of a magnetic resonance system is disclosed in DE 10 2005 056711 B3.
A wireless connection of local coils for an MR system is described therein. The coupling ensues either inductively or capacitively. The problem of making an electrical connection in the antenna devices that are intended for specific body parts, and that can be installed as needed in a magnetic resonance system, is not solved by this proposal. For example, for an antenna device adapted to the head shape for examinations of the head of a patient in a magnetic resonance system, the local coils are arranged closer to the tissue to be examined and thus ensure a stronger signal with better signal-to-noise ratio.
A radio-frequency device with coil that has a radio-frequency coil in order to receive a magnetic resonance signal and that has a second unit with a second radio-frequency coil with which the magnetic resonance signal is received independently of the first radio-frequency coil is known from US 2005/0242812 A1. The first and second units are supported by a carrier. The carrier can be detached from at least one of the first and second units. The carrier is configured such that the alignment of first unit in relation to the second unit can be changed.